Pub Date : 2024-06-28DOI: 10.1038/s44306-024-00022-7
Tatjana Thomas, Yassine Agarmani, Steffi Hartmann, Mark Kartsovnik, Natalia Kushch, Stephen M. Winter, Sebastian Schmid, Peter Lunkenheimer, Michael Lang, Jens Müller
Ferroelectricity, where electronic degrees of freedom determine the polar order—thereby enabling fast switching and phase control—is an important research field in current condensed-matter physics. Using a combination of resistance noise and dielectric spectroscopy we investigate the nature of relaxor-type electronic ferroelectricity in the organic conductor κ-(BETS)2Mn[N(CN)2]3, a system that represents a wider class of materials of correlated electron systems for which functionalities for organic spintronics recently have been discussed. The two complementary spectroscopies reveal a distinct low-frequency dynamics on different length scales, namely (i) an intrinsic relaxation that is typical for relaxor ferroelectrics which classifies the system as a possible new multiferroic, and (ii) two-level processes which we identify as fluctuating polar nanoregions (PNR), i.e., clusters of quantum electric dipoles that fluctuate collectively. The PNR preform above the metal insulator (MI) transition. Upon cooling through TMI, a drastic increase of the low-frequency 1/f-type fluctuations and slowing down of the charge carrier dynamics is accompanied by the onset of strong non-equilibrium dynamics indicating a glassy transition of interacting dipolar clusters. The freezing of PNR and non-equilibrium dynamics is suggested to be a common feature of organic relaxor-type electronic ferroelectrics.
{"title":"Slow and non-equilibrium dynamics due to electronic ferroelectricity in a strongly-correlated molecular conductor","authors":"Tatjana Thomas, Yassine Agarmani, Steffi Hartmann, Mark Kartsovnik, Natalia Kushch, Stephen M. Winter, Sebastian Schmid, Peter Lunkenheimer, Michael Lang, Jens Müller","doi":"10.1038/s44306-024-00022-7","DOIUrl":"10.1038/s44306-024-00022-7","url":null,"abstract":"Ferroelectricity, where electronic degrees of freedom determine the polar order—thereby enabling fast switching and phase control—is an important research field in current condensed-matter physics. Using a combination of resistance noise and dielectric spectroscopy we investigate the nature of relaxor-type electronic ferroelectricity in the organic conductor κ-(BETS)2Mn[N(CN)2]3, a system that represents a wider class of materials of correlated electron systems for which functionalities for organic spintronics recently have been discussed. The two complementary spectroscopies reveal a distinct low-frequency dynamics on different length scales, namely (i) an intrinsic relaxation that is typical for relaxor ferroelectrics which classifies the system as a possible new multiferroic, and (ii) two-level processes which we identify as fluctuating polar nanoregions (PNR), i.e., clusters of quantum electric dipoles that fluctuate collectively. The PNR preform above the metal insulator (MI) transition. Upon cooling through TMI, a drastic increase of the low-frequency 1/f-type fluctuations and slowing down of the charge carrier dynamics is accompanied by the onset of strong non-equilibrium dynamics indicating a glassy transition of interacting dipolar clusters. The freezing of PNR and non-equilibrium dynamics is suggested to be a common feature of organic relaxor-type electronic ferroelectrics.","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-11"},"PeriodicalIF":0.0,"publicationDate":"2024-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00022-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141537086","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-28DOI: 10.1038/s44306-024-00026-3
Cody Trevillian, Vasyl Tyberkevych
A general approach to quantify chirality, or absence of parity symmetry, of spin waves has been developed and applied to spin waves propagating in obliquely magnetized ferromagnetic films. Using theoretical arguments and numerical calculations, it is shown that, upon increasing spin wave wavevector, initially achiral spin waves develop chiral properties through the “parity exchange” mechanism, which implies, in particular, that chiral spin waves appear in pairs. The most striking example of the parity exchange mechanism is the simultaneous formation of two chiral waves: the magnetostatic surface wave and the recently discovered heterosymmetric spin wave, which were previously considered independent of each other. Another manifestation of the parity exchange is the formation of strongly chiral waves near the anti-crossings of spin wave branches of unequal symmetry. These findings illustrate viable paths to engineering spin wave systems with prescribed chiral spectra that had not previously been considered.
{"title":"Formation of chirality in propagating spin waves","authors":"Cody Trevillian, Vasyl Tyberkevych","doi":"10.1038/s44306-024-00026-3","DOIUrl":"10.1038/s44306-024-00026-3","url":null,"abstract":"A general approach to quantify chirality, or absence of parity symmetry, of spin waves has been developed and applied to spin waves propagating in obliquely magnetized ferromagnetic films. Using theoretical arguments and numerical calculations, it is shown that, upon increasing spin wave wavevector, initially achiral spin waves develop chiral properties through the “parity exchange” mechanism, which implies, in particular, that chiral spin waves appear in pairs. The most striking example of the parity exchange mechanism is the simultaneous formation of two chiral waves: the magnetostatic surface wave and the recently discovered heterosymmetric spin wave, which were previously considered independent of each other. Another manifestation of the parity exchange is the formation of strongly chiral waves near the anti-crossings of spin wave branches of unequal symmetry. These findings illustrate viable paths to engineering spin wave systems with prescribed chiral spectra that had not previously been considered.","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-8"},"PeriodicalIF":0.0,"publicationDate":"2024-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00026-3.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141537076","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-10DOI: 10.1038/s44306-024-00032-5
Elke Arenholz
{"title":"Celebrating 1 year of npj Spintronics","authors":"Elke Arenholz","doi":"10.1038/s44306-024-00032-5","DOIUrl":"10.1038/s44306-024-00032-5","url":null,"abstract":"","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2024-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00032-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141304305","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-03DOI: 10.1038/s44306-024-00020-9
Ryota Ono, Igor Solovyev, Sergey Artyukhin
Magnetoelectric multiferroics are key materials for next-generation spintronic devices due to their entangled magnetic and ferroelectric properties. Spiral multiferroics possess ferroelectric polarization and are particularly promising for electric control of magnetism and magnetic control of ferroelectricity. In this work, we uncover long-period incommensurate states characterized by unique multiferroic kinks in corundum nickelate Ni2InSbO6, a member of a promising family of polar magnets. Utilizing a 2-orbital S = 1 model, we derive formulas for Heisenberg and anisotropic magnetic exchanges and magnetically-induced polarization, enabling their calculations from first principles. We use these parameters in Monte Carlo and Landau theory-based calculations to reproduce experimentally observed magnetic structures and polarization dependence on the magnetic field. We predict magnetic phase transitions between flat spiral, conical spiral, canted antiferromagnetic and ferromagnetic states under increasing magnetic fields. Kinks in the spiral phases repel each other through a Yukawa-like potential arising from exchange of massive magnons. We also find that suitably directed electric fields can be used to stabilize the ferromagnetic and spiral states. The findings open a new pathway to predictive first-principles modelling of multiferroics and will inspire experiments and technological applications based on multiferroic kinks.
磁电多铁氧体具有纠缠磁性和铁电性能，是下一代自旋电子器件的关键材料。螺旋多铁氧体具有铁电极化特性，在电控磁和磁控铁电方面特别有前景。在这项研究中，我们发现了刚玉镍酸盐 Ni2InSbO6 中具有独特多铁氧体扭结特征的长周期非互斥态。利用 2 轨道 S = 1 模型，我们推导出了海森堡和各向异性磁交换以及磁致极化的公式，从而能够根据第一原理进行计算。我们在基于蒙特卡洛和朗道理论的计算中使用这些参数，再现了实验观察到的磁结构和极化对磁场的依赖性。我们预测了在磁场增大的情况下，平面螺旋、锥形螺旋、斜面反铁磁和铁磁态之间的磁相变。通过大质量磁子交换产生的类似尤卡瓦电势，螺旋相中的扭结相互排斥。我们还发现，适当定向的电场可用于稳定铁磁态和螺旋态。这些发现为多铁氧体的预测性第一原理建模开辟了一条新途径，并将激发基于多铁氧体扭结的实验和技术应用。
{"title":"Multiferroic kinks and spin-flop transition in Ni2InSbO6 from first principles","authors":"Ryota Ono, Igor Solovyev, Sergey Artyukhin","doi":"10.1038/s44306-024-00020-9","DOIUrl":"10.1038/s44306-024-00020-9","url":null,"abstract":"Magnetoelectric multiferroics are key materials for next-generation spintronic devices due to their entangled magnetic and ferroelectric properties. Spiral multiferroics possess ferroelectric polarization and are particularly promising for electric control of magnetism and magnetic control of ferroelectricity. In this work, we uncover long-period incommensurate states characterized by unique multiferroic kinks in corundum nickelate Ni2InSbO6, a member of a promising family of polar magnets. Utilizing a 2-orbital S = 1 model, we derive formulas for Heisenberg and anisotropic magnetic exchanges and magnetically-induced polarization, enabling their calculations from first principles. We use these parameters in Monte Carlo and Landau theory-based calculations to reproduce experimentally observed magnetic structures and polarization dependence on the magnetic field. We predict magnetic phase transitions between flat spiral, conical spiral, canted antiferromagnetic and ferromagnetic states under increasing magnetic fields. Kinks in the spiral phases repel each other through a Yukawa-like potential arising from exchange of massive magnons. We also find that suitably directed electric fields can be used to stabilize the ferromagnetic and spiral states. The findings open a new pathway to predictive first-principles modelling of multiferroics and will inspire experiments and technological applications based on multiferroic kinks.","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-10"},"PeriodicalIF":0.0,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00020-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141246220","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-03DOI: 10.1038/s44306-024-00024-5
Rana Saha, Holger L. Meyerheim, Börge Göbel, Ingrid Mertig, Stuart S. P. Parkin
Two-dimensional (2D) van der Waals (vdW) magnets that exhibit ferromagnetism at ambient temperature show great promise for spintronic applications. However, until now, only a few pristine or doped 2D magnets have demonstrated the ability to host non-collinear spin textures, thereby limiting their potential applications. Here we directly observe Néel-type skyrmions in the metallic vdW magnetic compound Fe3GaTe2 (FGaT) up to temperatures well above room temperature (≈340 K) in the absence of any external magnetic field. We show that the presence of defects in the structure of FGaT make its structure acentric and therefore compatible with hosting skyrmions that would otherwise not be possible. Indeed, in this regard it is very similar to the closely related compound Fe3GeTe2 (FGT), whose structure with the same space group P3m1 is also realized by defects. Interestingly, however, FGaT accommodates a significantly higher concentration of Fe within the vdW gaps, likely accounting for its enhanced Curie temperature (TC). In addition to the Néel skyrmions observed in the temperature range of 250–340 K, we also detect type-I and -II Bloch-type skyrmionic bubbles in the temperature range of 100–200 K due to an enhanced magnitude of dipole-dipole interactions relative to the Dzyaloshinskii-Moriya exchange interaction. Self-intercalation is thus a highly interesting property of vdW magnets that considerably modifies their fundamental properties.
在环境温度下表现出铁磁性的二维（2D）范德华（vdW）磁体为自旋电子应用带来了巨大前景。然而，到目前为止，只有少数原始或掺杂的二维磁体展示了承载非共线自旋纹理的能力，从而限制了它们的潜在应用。在这里，我们直接观察到金属 vdW 磁性化合物 Fe3GaTe2 (FGaT) 在没有任何外部磁场的情况下，温度远高于室温（≈340 K）时的奈尔型天线。我们的研究表明，FGaT 结构中存在的缺陷使其结构成为偏心结构，因此可以容纳天幕，而这在其他情况下是不可能的。事实上，在这一点上，它与密切相关的化合物 Fe3GeTe2 (FGT) 非常相似，后者的结构具有相同的空间群 P3m1，也是通过缺陷实现的。但有趣的是，FGaT 在 vdW 间隙中容纳了更高浓度的铁，这可能是其居里温度（TC）提高的原因。除了在 250-340 K 的温度范围内观察到的奈尔天电离外，我们还在 100-200 K 的温度范围内检测到了 I 型和 II 型布洛赫天电离气泡，这是因为相对于 Dzyaloshinskii-Moriya 交换相互作用，偶极-偶极相互作用的程度增强了。因此，自内闰是 vdW 磁体的一个非常有趣的特性，它极大地改变了 vdW 磁体的基本特性。
{"title":"High-temperature Néel skyrmions in Fe3GaTe2 stabilized by Fe intercalation into the van der Waals gap","authors":"Rana Saha, Holger L. Meyerheim, Börge Göbel, Ingrid Mertig, Stuart S. P. Parkin","doi":"10.1038/s44306-024-00024-5","DOIUrl":"10.1038/s44306-024-00024-5","url":null,"abstract":"Two-dimensional (2D) van der Waals (vdW) magnets that exhibit ferromagnetism at ambient temperature show great promise for spintronic applications. However, until now, only a few pristine or doped 2D magnets have demonstrated the ability to host non-collinear spin textures, thereby limiting their potential applications. Here we directly observe Néel-type skyrmions in the metallic vdW magnetic compound Fe3GaTe2 (FGaT) up to temperatures well above room temperature (≈340 K) in the absence of any external magnetic field. We show that the presence of defects in the structure of FGaT make its structure acentric and therefore compatible with hosting skyrmions that would otherwise not be possible. Indeed, in this regard it is very similar to the closely related compound Fe3GeTe2 (FGT), whose structure with the same space group P3m1 is also realized by defects. Interestingly, however, FGaT accommodates a significantly higher concentration of Fe within the vdW gaps, likely accounting for its enhanced Curie temperature (TC). In addition to the Néel skyrmions observed in the temperature range of 250–340 K, we also detect type-I and -II Bloch-type skyrmionic bubbles in the temperature range of 100–200 K due to an enhanced magnitude of dipole-dipole interactions relative to the Dzyaloshinskii-Moriya exchange interaction. Self-intercalation is thus a highly interesting property of vdW magnets that considerably modifies their fundamental properties.","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-7"},"PeriodicalIF":0.0,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00024-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141246232","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-03DOI: 10.1038/s44306-024-00018-3
Supriyo Bandyopadhyay
Magnetic straintronics made its debut more than a decade ago as an extremely energy-efficient paradigm for implementing a digital switch for digital information processing. The switch consists of a slightly elliptical nano-sized magnetostrictive disk in elastic contact with a poled ultrathin piezoelectric layer (forming a two-phase multiferroic system). Because of the elliptical shape, the nanomagnet’s magnetization has two stable (mutually antiparallel) orientations along the major axis, which can encode the binary bits 0 and 1. A voltage pulse of sub-ns duration and amplitude few to few tens of mV applied across the piezoelectric generates enough strain in the nanomagnet to switch its magnetization from one stable state to the other by virtue of the inverse magnetostriction (or Villari) effect, with an energy expenditure that is roughly an order of magnitude smaller than what it takes to switch a modern-day electronic transistor. That possibility, along with the fact that such a switch is non-volatile unlike the conventional transistor, generated significant excitement. However, it was later tempered by the realization that straintronic switching is also extremely error-prone, which may preclude many digital applications, particularly in Boolean logic. In this perspective, we offer the view that there is plenty of room for magnetic straintronics in the analog domain, which is much more forgiving of switching errors, and where the excellent energy-efficiency and non-volatility are a boon. Analog straintronics can have intriguing applications in many areas, such as a new genre of aggressively miniaturized electromagnetic antennas that defy the Harrington limits on the gain and radiation efficiency of conventional antennas, analog arithmetic multipliers (and ultimately vector matrix multipliers) for non-volatile deep learning networks with very small footprint and excellent energy-efficiency, and relatively high-power microwave oscillators with output frequency in the X-band. When combined with spintronics, analog straintronics can also implement a new type of spin field effect transistor employing quantum materials such as topological insulators, and they have unusual transfer characteristics which can be exploited for analog tasks such as frequency multiplication using just a single transistor. All this hints at a world of new possibilities in the analog domain that deserves serious attention.
十多年前，磁致伸缩技术作为一种极其节能的范例首次亮相，用于实现数字信息处理的数字开关。这种开关由一个略呈椭圆形的纳米级磁致伸缩盘与一个极化超薄压电层（形成两相多铁系统）弹性接触组成。由于是椭圆形，纳米磁体的磁化沿主轴有两个稳定（相互反平行）的方向，可以编码二进制位 0 和 1。在压电体上施加一个持续时间为亚纳秒、振幅为几毫伏到几十毫伏的电压脉冲，就能在纳米磁体中产生足够的应变，从而通过反向磁致伸缩（或维拉里）效应将磁化从一种稳定状态切换到另一种稳定状态，其能量消耗大约比现代电子晶体管的开关能量消耗小一个数量级。这种可能性，加上这种开关与传统晶体管不同，是非易失性的，引起了极大的轰动。然而，后来人们意识到应变电子开关也极易出错，这可能会排除许多数字应用，尤其是布尔逻辑应用，从而使人们的兴奋劲有所减弱。从这个角度来看，我们认为磁应变电子学在模拟领域还有很大的发展空间，因为模拟领域对开关误差的容忍度要高得多，而且卓越的能效和非波动性也是一大优势。模拟应变电子学在许多领域都有引人入胜的应用，例如，一种新型的极度微型化电磁天线，它打破了哈灵顿对传统天线增益和辐射效率的限制；用于非易失性深度学习网络的模拟算术乘法器（以及最终的矢量矩阵乘法器），具有极小的占地面积和出色的能效；以及输出频率在 X 波段的相对高功率微波振荡器。当与自旋电子学相结合时，模拟应变电子学还能利用量子材料（如拓扑绝缘体）实现一种新型自旋场效应晶体管，它们具有不同寻常的传输特性，可以仅利用单个晶体管来完成频率倍增等模拟任务。所有这些都预示着模拟领域将出现新的可能性，值得我们认真关注。
{"title":"Perspective: There is plenty of room for magnetic straintronics in the analog domain","authors":"Supriyo Bandyopadhyay","doi":"10.1038/s44306-024-00018-3","DOIUrl":"10.1038/s44306-024-00018-3","url":null,"abstract":"Magnetic straintronics made its debut more than a decade ago as an extremely energy-efficient paradigm for implementing a digital switch for digital information processing. The switch consists of a slightly elliptical nano-sized magnetostrictive disk in elastic contact with a poled ultrathin piezoelectric layer (forming a two-phase multiferroic system). Because of the elliptical shape, the nanomagnet’s magnetization has two stable (mutually antiparallel) orientations along the major axis, which can encode the binary bits 0 and 1. A voltage pulse of sub-ns duration and amplitude few to few tens of mV applied across the piezoelectric generates enough strain in the nanomagnet to switch its magnetization from one stable state to the other by virtue of the inverse magnetostriction (or Villari) effect, with an energy expenditure that is roughly an order of magnitude smaller than what it takes to switch a modern-day electronic transistor. That possibility, along with the fact that such a switch is non-volatile unlike the conventional transistor, generated significant excitement. However, it was later tempered by the realization that straintronic switching is also extremely error-prone, which may preclude many digital applications, particularly in Boolean logic. In this perspective, we offer the view that there is plenty of room for magnetic straintronics in the analog domain, which is much more forgiving of switching errors, and where the excellent energy-efficiency and non-volatility are a boon. Analog straintronics can have intriguing applications in many areas, such as a new genre of aggressively miniaturized electromagnetic antennas that defy the Harrington limits on the gain and radiation efficiency of conventional antennas, analog arithmetic multipliers (and ultimately vector matrix multipliers) for non-volatile deep learning networks with very small footprint and excellent energy-efficiency, and relatively high-power microwave oscillators with output frequency in the X-band. When combined with spintronics, analog straintronics can also implement a new type of spin field effect transistor employing quantum materials such as topological insulators, and they have unusual transfer characteristics which can be exploited for analog tasks such as frequency multiplication using just a single transistor. All this hints at a world of new possibilities in the analog domain that deserves serious attention.","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-15"},"PeriodicalIF":0.0,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00018-3.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141246208","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-03DOI: 10.1038/s44306-024-00013-8
M. B. Venuti, Xiyue S. Zhang, Eric J. Lang, Sadhvikas J. Addamane, Hanjong Paik, Portia Allen, Peter Sharma, David Muller, Khalid Hattar, Tzu-Ming Lu, Serena Eley
Skyrmions and antiskyrmions are nanoscale swirling textures of magnetic moments formed by chiral interactions between atomic spins in magnetic noncentrosymmetric materials and multilayer films with broken inversion symmetry. These quasiparticles are of interest for use as information carriers in next-generation, low-energy spintronic applications. To develop skyrmion-based memory and logic, we must understand skyrmion-defect interactions with two main goals—determining how skyrmions navigate intrinsic material defects and determining how to engineer disorder for optimal device operation. Here, we introduce a tunable means of creating a skyrmion-antiskyrmion system by engineering the disorder landscape in FeGe using ion irradiation. Specifically, we irradiate epitaxial B20-phase FeGe films with 2.8 MeV Au4+ ions at varying fluences, inducing amorphous regions within the crystalline matrix. Using low-temperature electrical transport and magnetization measurements, we observe a strong topological Hall effect with a double-peak feature that serves as a signature of skyrmions and antiskyrmions. These results are a step towards the development of information storage devices that use skyrmions and antiskyrmions as storage bits, and our system may serve as a testbed for theoretically predicted phenomena in skyrmion-antiskyrmion crystals.
{"title":"Inducing a tunable skyrmion-antiskyrmion system through ion beam modification of FeGe films","authors":"M. B. Venuti, Xiyue S. Zhang, Eric J. Lang, Sadhvikas J. Addamane, Hanjong Paik, Portia Allen, Peter Sharma, David Muller, Khalid Hattar, Tzu-Ming Lu, Serena Eley","doi":"10.1038/s44306-024-00013-8","DOIUrl":"10.1038/s44306-024-00013-8","url":null,"abstract":"Skyrmions and antiskyrmions are nanoscale swirling textures of magnetic moments formed by chiral interactions between atomic spins in magnetic noncentrosymmetric materials and multilayer films with broken inversion symmetry. These quasiparticles are of interest for use as information carriers in next-generation, low-energy spintronic applications. To develop skyrmion-based memory and logic, we must understand skyrmion-defect interactions with two main goals—determining how skyrmions navigate intrinsic material defects and determining how to engineer disorder for optimal device operation. Here, we introduce a tunable means of creating a skyrmion-antiskyrmion system by engineering the disorder landscape in FeGe using ion irradiation. Specifically, we irradiate epitaxial B20-phase FeGe films with 2.8 MeV Au4+ ions at varying fluences, inducing amorphous regions within the crystalline matrix. Using low-temperature electrical transport and magnetization measurements, we observe a strong topological Hall effect with a double-peak feature that serves as a signature of skyrmions and antiskyrmions. These results are a step towards the development of information storage devices that use skyrmions and antiskyrmions as storage bits, and our system may serve as a testbed for theoretically predicted phenomena in skyrmion-antiskyrmion crystals.","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-10"},"PeriodicalIF":0.0,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00013-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141246215","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-03DOI: 10.1038/s44306-024-00025-4
C. S. Davies, A. Kirilyuk
Over the last two decades, breakthrough works in the field of non-linear phononics have revealed that high-frequency lattice vibrations, when driven to high amplitude by mid- to far-infrared optical pulses, can bolster the light-matter interaction and thereby lend control over a variety of spontaneous orderings. This approach fundamentally relies on the resonant excitation of infrared-active transverse optical phonon modes, which are characterized by a maximum in the imaginary part of the medium’s permittivity. Here, in this Perspective article, we discuss an alternative strategy where the light pulses are instead tailored to match the frequency at which the real part of the medium’s permittivity goes to zero. This so-called epsilon-near-zero regime, popularly studied in the context of metamaterials, naturally emerges to some extent in all dielectric crystals in the infrared spectral range. We find that the light-matter interaction in the phononic epsilon-near-zero regime becomes strongly enhanced, yielding even the possibility of permanently switching both spin and polarization order parameters. We provide our perspective on how this hitherto-neglected yet fertile research area can be explored in future, with the aim to outline and highlight the exciting challenges and opportunities ahead.
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Pub Date : 2024-06-03DOI: 10.1038/s44306-024-00017-4
Kouki Nakata, Kei Suzuki
There has been a growing interest in non-Hermitian quantum mechanics. The key concepts of quantum mechanics are quantum fluctuations. Quantum fluctuations of quantum fields confined in a finite-size system induce the zero-point energy shift. This quantum phenomenon, the Casimir effect, is one of the most striking phenomena of quantum mechanics in the sense that there are no classical analogs and has been attracting much attention beyond the hierarchy of energy scales, ranging from elementary particle physics to condensed matter physics, together with photonics. However, the non-Hermitian extension of the Casimir effect and the application to spintronics have not yet been investigated enough, although exploring energy sources and developing energy-efficient nanodevices are its central issues. Here we fill this gap. By developing a magnonic analog of the Casimir effect into non-Hermitian systems, we show that this non-Hermitian Casimir effect of magnons is enhanced as the Gilbert damping constant (i.e., the energy dissipation rate) increases. When the damping constant exceeds a critical value, the non-Hermitian Casimir effect of magnons exhibits an oscillating behavior, including a beating one, as a function of the film thickness and is characterized by the exceptional point. Our result suggests that energy dissipation serves as a key ingredient of Casimir engineering.
{"title":"Non-Hermitian Casimir effect of magnons","authors":"Kouki Nakata, Kei Suzuki","doi":"10.1038/s44306-024-00017-4","DOIUrl":"10.1038/s44306-024-00017-4","url":null,"abstract":"There has been a growing interest in non-Hermitian quantum mechanics. The key concepts of quantum mechanics are quantum fluctuations. Quantum fluctuations of quantum fields confined in a finite-size system induce the zero-point energy shift. This quantum phenomenon, the Casimir effect, is one of the most striking phenomena of quantum mechanics in the sense that there are no classical analogs and has been attracting much attention beyond the hierarchy of energy scales, ranging from elementary particle physics to condensed matter physics, together with photonics. However, the non-Hermitian extension of the Casimir effect and the application to spintronics have not yet been investigated enough, although exploring energy sources and developing energy-efficient nanodevices are its central issues. Here we fill this gap. By developing a magnonic analog of the Casimir effect into non-Hermitian systems, we show that this non-Hermitian Casimir effect of magnons is enhanced as the Gilbert damping constant (i.e., the energy dissipation rate) increases. When the damping constant exceeds a critical value, the non-Hermitian Casimir effect of magnons exhibits an oscillating behavior, including a beating one, as a function of the film thickness and is characterized by the exceptional point. Our result suggests that energy dissipation serves as a key ingredient of Casimir engineering.","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-6"},"PeriodicalIF":0.0,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00017-4.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141246228","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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